Free fatty acids and automatic milking systems

With the introduction of automatic milking (AM) systems, increased levels of free fatty acids (FFA) in milk were observed, which might result in off-flavours in milk and dairy products. The aim of this study was to investigate the factors contributing to elevated FFA levels: influence of the milking frequency, technical parameters of the automatic milking system, and finally, farm management aspects.

Milking frequency was studied in a Latin square design with milking intervals of 4, 8 and 12 hours and showed increased FFA -levels for the shorter intervals. Milk fat and protein percentages of milk were equal. Milking frequencies are of more importance than technical parameters of the AM system, because FFA levels for farms milking three times per day and AM systems are more or less comparable. However, technical aspects cannot be excluded. Compared to conventional milking, the air/milk ratio is higher, probably resulting in more disruption of milk fat globule membranes. Technical factors were studied in a laboratory study using milking machine components of two AM-systems and of a conventional system. The milking machine components of one AM-system caused an extra increase of 0,09 mmol/100 g fat compared with the conventional milking sys- tem. These differences were found using susceptible milk. Susceptible milk is defined as milk with a high initial FFA level, caused by e.g. short milking interval or end of lactation of the cow. The other AM milking machine also caused a significant increase in FFA levels compared to a conventional system, but this increase was due to different FFA levels at the start of the experiment.

FFA levels of samples taken before, during and after milking indicated that taking mixed milk samples per cow was the most representative way of sampling. Therefore mixed milk samples were taken to determine FFA levels during the rest of the experiments. Fat globule size diameters were determined in milk of six cows. Relations between average globule size and FFA were not found. A linear relation between fat production and average globule size was indicated (P=0.051) with a percentage variance accounted for of 56,9%. Linear regression showed no significant relations between FFA and fatty acid composition of the milk of the six cows sampled. For milk yield and lactation stage of the cows significant relations were found for some fatty acids. However, results should be interpreted with care, they were based on six cows from one farm.

Apart from milking frequencies and technical parameters, management aspects probably play a role. In a study on variation of FFA levels, 12 farms were monthly sampled. Results showed more variation at higher FFA lev- els, as was expected. But on conventional farms milking twice a day (2x) high FFA levels were caused by tech- nical factors (high level milk lines in stanchion barns). On farms milking three times a day (3x) FFA levels were relatively high and causes could not be defined in all cases. Similarity between grazing and high FFA levels was found on two of the four investigated farms. On AM farms, low FFA levels were possible throughout the year, depending on the farm tested. On one farm, high FFA levels were due due to a high percentage of failed milk- ings. Reduction of the number of failed milkings reduced the high FFA level to an acceptable level.

In a study on management factors on eight AM farms and on six farms milking 3x with determination of FFA level on two moments (within six weeks in autumn), the differences between high and low FFA level farms were bigger for farms milking 3x than for AM farms with the same AM brand and cooling system. On farms milking 3x with high FFA levels, quota and number of cows on the farm were significant lower than on farms with low FFA levels. These differences were not found on AM farms.

Susceptibility of cows for lipolysis is very important, but it is a complex matter. Known causes are lactation stage, pregnancy stage and milking frequency. Although feeding and animal health play a role in increased FFA levels, more fundamental research is needed regarding this susceptibility of cows.
Although several FFA problems were solved by adjusting milking frequencies and technical adjustments, in some situations high FFA levels remained. Other farm management aspects, like feeding regime, breeding and animal health are still subject of ongoing research and results will be incorporated in future papers.

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